Method and Apparatus for Utilizing Multiple Carriers in High Speed Packet Access Communications

1. A method, implemented in a wireless transmit/receive unit (WTRU), for utilizing multiple carriers, the method comprising: monitoring, by the WTRU with a receiver capable of receiving on one downlink carrier at a time, a scheduling channel on a first downlink carrier; receiving an indication via the scheduling channel to receive data on a second downlink carrier; switching from the first downlink carrier to the second downlink carrier and receiving the data; and switching from the second downlink carrier to the first downlink carrier, wherein the WTRU resumes monitoring the scheduling channel.

2. The method of claim 1 wherein the switching is from an anchor carrier to a non-anchor carrier at a high speed shared control channel (HS-SCCH) sub-frame boundary, and further comprising switching from the non-anchor carrier to the anchor carrier at an end of a subsequent high speed physical downlink shared channel (HS-PDSCH) subframe.

3. The method of claim 1 wherein the switching is performed at a high speed physical downlink shared channel (HS-PDSCH) sub-frame boundary.

4. The method of claim 1 wherein the switching is performed after a guard interval.

5. The method of claim 4 wherein the WTRU interprets a missing E-DCH HARQ indicator channel (E-HICH) during the guard interval as a negative acknowledge (NACK).

6. The method of claim 4 wherein the WTRU does not transmit in a hybrid automatic repeat request (HARQ) process that has its corresponding E-DCH HARQ indicator channel (E-HICH) falling during the guard interval.

7. A wireless transmit/receive unit (WTRU) for utilizing multiple carriers, the WTRU comprising: a receiver configured to receive on one downlink carrier at a time; and a processor configured to monitor a scheduling channel on a first downlink carrier; wherein: the receiver is further configured to receive an indication via the scheduling channel to receive data on a second downlink carrier; the processor is further configured to switch from the first downlink carrier to the second downlink carrier, wherein the receiver is configured to receive the data; and the processor is further configured to switch from the second downlink carrier to the first downlink carrier, wherein the WTRU resumes monitoring the scheduling channel.

8. The WTRU of claim 7 wherein the the switch from the first downlink carrier to the second downlink carrier is from an anchor carrier to a non-anchor carrier at a high speed shared control channel (HS-SCCH) sub-frame boundary, and wherein the processor is further configured to switch from the non-anchor carrier to the anchor carrier at an end of a subsequent high speed physical downlink shared channel (HS-PDSCH) subframe.

9. The WTRU of claim 7 wherein the the switch is performed at a high speed physical downlink shared channel (HS-PDSCH) sub-frame boundary.

10. The WTRU of claim 7 wherein the the switch is performed after a guard interval.

11. The WTRU of claim 10 wherein the processor is further configured to interpret a missing E-DCH HARQ indicator (E-HICH) during the guard interval as a negative acknowledgement (NACK).

12. The WTRU of claim 10 wherein the processor is configured to not transmit in a hybrid automatic repeat request (HARQ) process that has its corresponding E-DCH HARQ indicator channel (E-HICH) falling during the guard interval.